1. Field of the Invention
The present invention relates to inspection of a product and a process for producing a concave-convex pattern shape such as on a hard disk medium, and to a technique for inspecting a defect, deformation, and dimension measurement of the pattern shape.
2. Description of the Related Art
In recent years, hard disks as recording media for use in computers have been increasing in capacity. For increases in the capacity of recording information, it is essential to increase the recording density of a disk. As a method for greatly increasing the recording density compared to conventional disk media, patterned media having patterns formed on the disk surface are showing great promise. To form patterned media, a nanoimprint technique for forming nano-order patterns at low cost is used. In the nanoimprint technique, a prepared stamp is pressed against material to duplicate the same pattern as the stamp. With the nanoimprint technique, the formation of optical elements and an alternative to a semiconductor exposure process as well as patterned media for HDDs have been studied.
In general, pattern dimensions for use in patterned media are less than 100 nm, that is, less than the wavelengths of visible light. This exceeds the resolution limit of an optical system such as an ordinary microscope, so that the system cannot directly capture a pattern shape. Accordingly, shape measurement by an AFM, measurement by a SEM, or near-field light detection by an SNOM or the like can be considered; however, from the viewpoint of throughput, none of them makes it possible to observe a wide area at high speed.
On the other hand, in semiconductor patterning process control, an optical inspection apparatus of scatterometry theory is applied. With this, a periodic pattern such as a line-and-space pattern is detected using a control pattern called a TEG pattern disposed beforehand in an area other than a product, on a semiconductor wafer. For example, according to this method, white light is applied to a periodic pattern in an area of more than about 50 μm square, and the spectral characteristics of the reflected light are detected, so that the shape of the observation pattern is calculated. Japanese Patent Application Laid-Open No. 2007-133985 discloses a patterned media inspection according to this method. In accordance therewith, detected light reflection intensity is analyzed with the scatterometry method, thereby making it possible to measure and evaluate the shape of a periodic pattern. Further, in the case where servo information sections exist on a sample, analyzing acquired data enables similar evaluation.
U.S. Pat. No. 6,639,663 describes a method for utilizing a detection tool according to the scatterometry method to classify semiconductor defects.
The details of optical scatterometry are described in Proceedings of SPIE, Vol. 4344, pp. 716-725 (2001) and Applied Optics, Vol. 37, pp. 5112-5115 (1998). In short, light is applied to a one-dimensional periodic structure, and dependency on an incident angle, a wavelength, a polarization direction, and a reflection order in the intensity distribution of the reflected light is checked, thereby obtaining information such as the dimensions, space period, cross-section shape, and optical property of the periodic structure. According to this method, it is possible to detect a minute difference, a particle, or a defect in a periodic structure smaller than the wavelength of light.